Narrative:

After a normal takeoff and after the climb check; the first officer noticed a red indicated airspeed indication on both the captain's and first officer's pfds. This was confirmed by an indicated variance of around 10-20 KTS between the indicated airspeeds on each side. We continued to climb and watch as it seemed to remain within this parameter until around 8;000-10;000 ft when we started getting all kinds of alert indications. We started with the autopilot failing; the autothrottles failing; low speed protection warnings; the altitude alerter; half the fcp; both flight directors; a level 2 rudder limiter fail; and many other level 1 alerts. The first officer was flying so I started; from top to bottom; addressing the alerts using the QRH and realized that all these alerts were a result of something much bigger. The airspeed indications continued to get more unreliable and the captain's primary flight display at one point indicated 320 KTS while the first officer's indicated 240 KTS. Because of the seriousness of the erroneous airspeed indications and not having full trust in the airspeed indications; I chose to declare an emergency and return to ZZZ. Also; because the errors kept going away and coming back with the consequences messages getting more lengthy with each sequence; I decided we should get on the ground before we lost all reliable airspeed indications; so after discussing the matter with maintenance; I decided to perform an overweight landing. I briefed the flight attendants and the passengers that we were returning to ZZZ and after all appropriate checklists were run; I took control of the aircraft; since I was more confident in making a smooth touchdown that was especially important with our 108;000 pound landing weight. At around 7-8 mile final; all indications and alerts returned to normal; we retained our emergency status until touchdown; although we never asked that the crash trucks be 'rolled.' the landing was a 'greaser' and returned to the gate with no further incident. I do not know the final cause of this occurrence; although I did hear the mechanic state that he had noticed the air data inertial reference unit (adiru) #1's internal fan was inoperative on his initial check in the east&east compartment. There were also many related issues that had been written up during flights prior to our flight that had been signed off just prior to us taking the airplane. I believe they were related to fccs and rvsm and other similar electronic type issues.

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Original NASA ASRS Text

Title: B717-200 returns to departure airport following multiple system warnings apparently the result of problems with an ADIRU.

Narrative: After a normal takeoff and after the climb check; the First Officer noticed a red indicated airspeed indication on both the Captain's and First Officer's PFDs. This was confirmed by an indicated variance of around 10-20 KTS between the indicated airspeeds on each side. We continued to climb and watch as it seemed to remain within this parameter until around 8;000-10;000 FT when we started getting all kinds of alert indications. We started with the autopilot failing; the autothrottles failing; low speed protection warnings; the altitude alerter; half the FCP; both flight directors; a level 2 rudder limiter fail; and many other level 1 alerts. The First Officer was flying so I started; from top to bottom; addressing the alerts using the QRH and realized that all these alerts were a result of something much bigger. The airspeed indications continued to get more unreliable and the Captain's Primary Flight Display at one point indicated 320 KTS while the First Officer's indicated 240 KTS. Because of the seriousness of the erroneous airspeed indications and not having full trust in the airspeed indications; I chose to declare an emergency and return to ZZZ. Also; because the errors kept going away and coming back with the consequences messages getting more lengthy with each sequence; I decided we should get on the ground before we lost all reliable airspeed indications; so after discussing the matter with maintenance; I decided to perform an overweight landing. I briefed the Flight Attendants and the passengers that we were returning to ZZZ and after all appropriate checklists were run; I took control of the aircraft; since I was more confident in making a smooth touchdown that was especially important with our 108;000 LB landing weight. At around 7-8 mile final; all indications and alerts returned to normal; we retained our emergency status until touchdown; although we never asked that the crash trucks be 'rolled.' The landing was a 'greaser' and returned to the gate with no further incident. I do not know the final cause of this occurrence; although I did hear the Mechanic state that he had noticed the Air Data Inertial Reference Unit (ADIRU) #1's internal fan was inoperative on his initial check in the E&E compartment. There were also many related issues that had been written up during flights prior to our flight that had been signed off just prior to us taking the airplane. I believe they were related to FCCs and RVSM and other similar electronic type issues.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.